Lubrication is essential for ensuring proper operation of a bearing. It is therefore desirable in many applications to monitor the lubricant within the bearing, so that a re-lubrication action can be initiated if, for example, the lubricant contains an unacceptable level of water or particulate contamination.
A device for determining metallic contaminant particles in lubricating grease is disclosed in WO 2006/075049. A sample of grease is first taken from e.g. a bearing to allow the determination to be made. The device comprises a sensor with a core, on which the measured grease sample is placed, and a sensor coil which is wound around the core. The device also comprises an alternating current source for supplying the operating voltage and an inductance measurement bridge for determining the change of the impedance of the sensor coil, when a sample of lubricating grease containing contaminating particles is applied on the sensor, and for outputting a differential output signal.
A drawback of this solution is that a sample of grease must be taken from the bearing. In many applications, this is inconvenient or may be impossible due to the inaccessibility of the bearing.
A further example of a measurement apparatus for analysis of a lubricant of a bearing is known from U.S. Pat. No. 8,624,191. The apparatus comprises a transmitter, a receiver and a sample area, which is arranged in front of the transmitter and the receiver. The sample area is arranged at least partly within the bearing interior, which is filled with a lubricant. The sample area, the transmitter, and the receiver are configured with a diffuse reflection geometry so that the transmitter irradiates the sample area with e.g. IR light and the receiver receives diffuse reflection of the IR light from the sample area, which is then used to measure deterioration of the lubricant.
There is room for improvement.